Vinblastine (vincaleucoblastine or VLB) was isolated by Beer et al., U.S. Pat. No. 3,097,137, by extraction of Vinca rosea leaves with ethanol and acetic acid, acidification of the extract with hydrochloric acid, extraction of the acidic aqueous solution with benzene followed by pH gradient elution chromatography of the benzene-extracted alkaloids over alumina. An improved process for preparing vinblastine and its companion alkaloid, leurosine, is contained in Svoboda, U.S. Pat. No. 3,225,030. According to the process of this patent, the leaves of Vinca rosea are extracted into a tartaric acid-benzene solvent system, the benzene layer is neutralized, the base-insoluble alkaloids are extracted into benzene, and the benzene extract is then subjected to a chromatographic separation procedure in which leurosine and vinblastine are successively eluted. The separation of vincristine (leurocristine) from other dimeric Vinca alkaloids is described in Svoboda et al., U.S. Pat. No. 3,205,220. Here again Vinca rosea leaves are extracted with a mixture of benzene and tartaric acid. The mother liquors eventually obtained after crystallization of vinblastine sulfate by either of the procedures of the above two patents are subjected to a citric acid extraction procedure first at pH = 4.4 and then at pH = 7.0. The alkaloids obtained by evaporation of the benzene eluant at this higher pH are chromatographed over deactivated alumina, and vincristine is eluted after vinrosidine (leurosidine).
More recently, West German Pat. No. 2,124,023 describes a process for purifying the three principle dimeric anti-cancer alkaloids of Vinca rosea: vinblastine, vincristine and leurosine. According to the process of this patent, vinca leaves are extracted with aqueous methanol and the dimeric alkaloids thus extracted are converted to acid addition salts in solution, preferably sulfates. The acidic extract is then extracted with benzene, the benzene extracts being discarded. The acidic layer is next made alkaline and the alkaloids extracted into benzene. This benzene extract is evaporated to dryness and the residual alkaloids again converted to the corresponding sulfate salts with 10 percent sulfuric acid. A mixture of the crystalline sulfates of the 3-dimeric alkaloids is obtained, and these are separated by chromatography using methylenechloride and chloroform as the elution solvents. Alternatively, the alkaloidal bases are separated by chromatography without first converting them to sulfate salts.
Finally, Hungarian Pat. No. 154,715 published 11-22-67 describes a process in which vinca leaves are treated with ammonium hydroxide, and then with toluene. The toluene extract is contacted with hydrochloric acid, and the remaining alkaloid mixture extracted with ethylenedichloride at pH =9. This alkaloid fraction is then chromatographed over neutral alumina. The vinblastine and leurosine fractions are eluted with benzene-ether. (No mention is made of the isolation of vincristine in this particular patent). The methanol extraction procedure outlined in West German Pat. No. 2,124,023 is also disclosed in the aforesaid Hungarian patent.
It is an object of this invention to provide a process for the purification of vincristine, des-N-methylvinblastine and vinblastine starting with Vinca rosea leaves, which process yields the desired dimeric alkaloids in greater quantity and with a higher degree of purity than any of the previously described processes.